As one of the main sources of antimicrobial substances, polymorphonuclear leukocytes (PMN) are critical for phagocytosis and killing of microbs for protection of animals against invading pathogens. Despite of their importance, there are many unknown events on neutrophils and leukocytes in domestic animals, especially in the effect of environmentally-originated mycotoxins. As one of the most dangerous and hazardous aflatoxins (AFs), AFB1 are thought to be a potent immunotoxic; it is hardly degraded in the body and environment (biosphere). To investigate the effect of AFB1 on blood PMN functions, for the first time we examined the in vitro effects of the naturally-occurring doses of AFB1 on the mechanisms of free radicals production (phagocytosis and non-phagocytosis dependent-luminal-and-isoluminol chemiluminescence (CL)), phagocytic and killing activities against Staphylococcus (S.) aureus and Escherichia (E.) coli and on the necrosis and apoptosis of PMN. Healthy dairy cows were used as a source of PMN. The isolated blood PMN were exposed with 0, 0.01, 0.05 and 0.5 ng/ml of AFB1 for 0.5, 3 and 18 hours depending on the assay; their capacity to kill E. coli and S. aureus was then examined by a bactericidal assay using sample cultivation. Though the effect of extremely low doses of AFB1 were less pronounced, at 0.5 ng/ml the production of free radicals was greatly enhanced, especially extracellularly. In contrast to isoluminol-enhanced CL, the AFB1-treated PMN showed a remarkably diminished phagocytosis-depended luminal-enhanced CL. The % killing of E. coli and S. aureus by AFB1-treated PMN was significantly lower than those of non-treated ones. Our results confirm the prooxidant, antiphagocytic and slight antinecrotic properties of permissible doses of AFB1 for bovine PMN. Although this effect may seem invisible in the farms, the scope of the suppressive effects of the permissible levels of AFB1 on cellular part of circulating innate immunity would be alarming for farm animals and public health.

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